1. Field of the Inventions
The present inventions relate to power transmitting apparatuses for arbitrarily transmitting or cutting-off a rotational force of the input member to or from the output member.
2. Description of the Related Art
In general, power transmission apparatuses for motorcycles are intended to arbitrarily transmit or cut-off a power of an engine to a transmission and a driving wheel. Such power transmission apparatuses typically comprise an input member connected to an engine side, an output member connected to the transmission and the driving wheel side, and a clutch member connected to the output member. The power can be transmitted by pressing together a plurality of driving clutch plates and driven clutch plates and cut-off by releasing the pressure force between the plates.
For example as disclosed in Japanese Laid-open Patent Publication No. 150517/1990, cams are provided for increasing the pressure-contacting force between the driving and driven clutch plates during an ordinary power transmitting phase and the other function, i.e. back-torque limiting function for releasing the driving and driven clutch plates when the rotational speed of an output member has exceeded the rotational speed of an input member. In such a power transmitting apparatus, the cams are formed by gradient surfaces (cam surfaces) formed on the pressure plate and the clutch member.
According to the power transmitting apparatus of this prior art, one set of cam surfaces (pressure-contact assisting cam surfaces) act in an ordinary power transmitting mode to move a pressure plate toward a direction in which both the driving and driven clutch plates are strongly pressed to each other, and on the contrary, in a back-torque absorbing mode the other set of cam surfaces (back-torque limiting cam surfaces) act to move the pressure plate toward a direction in which the pressure-contact between the driving and driven clutch plates are released.